Phenol is an important product in the chemical industry and is useful in, for example, the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and plasticizers.
Currently, the most common route for the production of phenol is the Hock process. This is a three-step process in which the first step involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone. However, the world demand for phenol is growing more rapidly than that for acetone. In addition, due to a developing shortage, the cost of propylene is likely to increase. Thus, a process that uses higher alkenes instead of propylene as feed and co-produces higher ketones, rather than acetone, may be an attractive alternative route to the production of phenols.
One such process proceeds via cyclohexylbenzene, followed by the oxidation of the cyclohexylbenzene to cyclohexylbenzene hydroperoxide, which is then cleaved to produce phenol and cyclohexanone in substantially equimolar amounts Although various methods are available for the production of cyclohexylbenzene, a preferred route is disclosed in U.S. Pat. No. 6,037,513, in which the cyclohexylbenzene is produced by hydroalkylating benzene with hydrogen in the presence of a bifunctional catalyst comprising a molecular sieve of the MCM-22 family and at least one hydrogenation metal selected from palladium, ruthenium, nickel, cobalt and mixtures thereof. The '513 patent also discloses that the resultant cyclohexylbenzene can be oxidized to the corresponding hydroperoxide and then decomposed to the desired phenol and cyclohexanone co-product.
One of the problems associated with producing cyclohexylbenzene by hydroalkylation of benzene is that economically viable commercial sources of hydrogen contain inert materials, such as methane, nitrogen, ethane, and propane. Being inert, these materials do not participate in the hydroalkylation reaction but, as hydrogen is consumed, they build up and must be purged. However, direct purging from, for example, the unreacted hydrogen recycle line to the hydroalkylation reactor also vents expensive hydrogen. Moreover, such a purge gas would contain benzene that would have to be removed before the purge could be vented to atmosphere.
There is therefore a need for an inexpensive process for removing inerts from the hydrogen recycle streams employed in the hydroalkylation of benzene, which method minimizes loss of useful hydrogen and benzene. The present invention seeks to provide such a process.